1. Three –line system. The hybrid seed production involves multiplication of cytoplasmic – genetic male sterile line (A line) , maintainer line ( B line) and a restore line ( R line) and production of F1 hybrid seed ( AXR).

2. Two-line system. The hybrid seed production involves the use of photo-period sensitive genetic male sterile (PSMS). Any normal line can serve as a restorer.

3. By using chemical emasculators. Chemicals that can sterilize the stamen, with little or no effect on the normal functioning of the pistil, can be used to emasculate female parents for hybrid rice production. The advantages are obvious, no special development of male sterile or restore lines is required and extensive varietal resources are available.

Chemical emasculators such as male gametocide 1 (ME1) and male gametocide 2 ( MG2) were developed in China and have been successfully used in hybrid rice production.

In chemical emasculation, physiological male sterility is artificially created by spraying the rice plant with chemicals to induce stamen sterility without harming the pistil. In hybrid seed production , two – varieties are planted in alternate strips, and one is chemically sterilized and pollinated by the other.